The crystal growth velocity of Ni95Si5 and Ni90Si10 alloys as a function
of undercooling is investigated using molecular dynamics simulations.
The modified imbedded atom method potential yields the equilibrium
liquidus temperatures T-L approximate to 1505 and 1387K for Ni95Si5 and
Ni90Si10 alloys, respectively. From the liquidus temperatures down to
the deeply undercooled region, the crystal growth velocities of both the
alloys rise to the maximum with increasing undercooling and then drop
slowly, whereas the athermal growth process presented in elemental Ni is
not observed in Ni-Si alloys. Instead, the undercooling dependence of
the growth velocity can be well-described by the diffusion-limited
model, furthermore, the activation energy associated with the diffusion
from melt to interface increases as the concentration increases from 5
to 10 at.% Si, resulting in the remarkable decrease of growth velocity.